(1)
Division of Public Health Sciences, Wake Forest School of Medicine, Winston-Salem, NC, USA
Synopsis
Ventricular conduction defects considered include left bundle branch block (LBBB), isolated right bundle branch block (RBBB), bifascicular block (RBBB with left anterior or left posterior fascicular block (LAFB and LPFB, respectively) and indetermined type ventricular conduction defect (IVCD).
In the Women’s Health Initiative (WHI) study CHD mortality was increased for LBBB over threefold in CHD-free women and nearly threefold in women with CVD. The CHD mortality risk for isolated RBBB was increased significantly (1.62-fold) only in women with CVD as was the risk for IVCD (1.62-fold increase). The risk for all-cause mortality was increased significantly in women with CVD at baseline for LBBB (1.43-fold) and for bifascicular block (2.69-fold) but not in any other subgroup by bundle branch block category and CVD status.
The risk for incident HF was evaluated in another WHI study. Compared to women with no bundle branch block, LBBB and IVCD were strong predictors of incident HF. RBBB was not a significant predictor of incident HF in multivariable-adjusted risk model but RBBB combined with LAFB was a strong predictor. QRS duration was an independent predictor of incident HF only in LBBB, with more pronounced risk for QRS ≥140 ms than for <140 ms. QRS nondipolar voltage (RNDPV) was an independent predictor in both RBBB and LBBB and in LBBB in addition, spatial QRS/T angle and ST J-point depression in aVL were independent predictors.
Repolarization abnormalities in bundle branch blocks are generally considered as strictly secondary to increased QRS duration and altered spatial sequence of depolarization and consequently clinically of little diagnostic or prognostic utility. This chapter covers more recent studies which demonstrate that repolarization abnormalities also in bundle branch blocks are important predictors of increased risk of coronary heart disease (CHD) and cardiovascular disease (CVD) mortality and adverse events such as heart failure (HF).
Abbreviations and Acronyms
ARIC
Arteriosclerosis research in communities study
CHD
Coronary heart disease
HF
Heart failure
HR
Hazard ratio
IVCD
Indetermined type ventricular conduction defect
LAFB
Left anterior fascicular block
LBBB
Left bundle branch block
LPFB
Left posterior fascicular block
RBBB
Right bundle branch block
RNDPV
QRS nondipolar voltage
Rp
R wave peak in the spatial QRS vector magnitude function
Tp
T wave peak in the spatial T vector magnitude function
VCD
Ventricular conduction defect
WHI
Women’s Health Initiative
Ѳ(Rm|Tm)
Spatial angle between the mean QRS and ST-T vectors
Ѳ(Rp|Tp)
Spatial angle between the peak QRS and peak T vectors
Ѳ(Tinit|Tterm)
Spatial angle between the initial and terminal T vectors
8.1 Introduction
Repolarization abnormalities in bundle branch blocks (BBB) are generally considered as strictly secondary to increased QRS duration and altered spatial sequence of depolarization and clinically of little diagnostic or prognostic utility. More recent studies covered in this chapter have demonstrated that repolarization abnormalities in BBB are important predictors of increased risk of coronary heart disease (CHD) and cardiovascular disease (CVD) mortality and adverse events such as heart failure (HF). BBBs considered in this chapter include left and right BBB (LBBB and RBBB, respectively, indetermined type ventricular conduction defect (IVCD) and bifascicular block (RBBB combined with left anterior fascicular block (LAFB) or left posterior fascicular block (LPFB)). The prevalence and the mortality risk for ventricular conduction defects from epidemiological studies before 2007 was covered previously [1].
BBBs induce various degrees of repolarization changes ranging from relatively minor, mainly terminal repolarization changes in RBBB to profound repolarization changes in LBBB.
8.2 Ventricular Conduction Defects, Repolarization Abnormalities and Mortality Risk in Women
New information about the mortality risk and the risk of incident heart failure (HF) specifically in women has emerged from the Women’s Health Initiative study reports [2, 3]. The mortality risk findings in bundle branch blocks will be addressed here first.
In the report of Zhang et al. [2] 66,450 WHI women were followed for 14 years. The risk for CVD death and deaths from all causes was evaluated for women with and without CVD at the baseline. Table 8.1 reproduced from Table 2 of Zhang et al. summarizes the results for LBBB and RBB. There were 714 women with LBBB at baseline and RBBB was coded in 832 women. Focusing on risk models multivariable-adjusted for demographic and clinical risk factors, the highlights of the findings were the following:
Table 8.1
Hazard ratios with 95 % confidence intervals for coronary heart disease death for bundle branch block categories by baseline cardiovascular disease status
CVD status | Category | Event rate | Univariate | Multivariatea |
|---|---|---|---|---|
CVD-free | No BBB | 894/52,663(1.7 %) | HR = 1 | HR = 1 |
LBBB | 24/408 (5.9 %) | 2.40 (1.60–3.61) | 2.17 (1.37–3.43) | |
RBBB | 21/534 (3.9 %) | 1.68 (1.09–2.59) | 1.31 (0.77–2.23) | |
CVD | No BBB | 597/12,048 (5.0 %) | HR = 1 | HR = 1 |
LBBB | 48/306 (15.7 %) | 2.85 (2.12–3.82) | 2.92 (2.08–4.08) | |
RBBB | 27/298 (9.1 %) | 1.60 (1.09–2.36) | 1.62 (1.08–2.43) | |
IVCD | 10/73 (13.7 %) | 2.72 (1.46–5.08) | 2.52 (1.34–4.75) | |
RBBB & LAFB | 5/31 (16.1 %) | 2.87 (1.19–6.92) | 3.09 (1.26–7.58) |
The risk for CHD-death for LBBB was increased 2.17-fold for women free from cardiovascular disease (CVD) and nearly threefold (HR 2.92, CI 2.08–4.08) for women with CVD. The risk for all-cause mortality was increased significantly for LBBB in women with CVD at baseline (HR 1.43, CI 1.11–1.83); the risk for all-cause mortality was not significantly increased in any other subgroup by bundle branch block category and CVD status. For isolated RBBB the risk for CHD death was significantly increased only in women with CVD (HR 1.62, CI 1.08–2.43). For RBBB combined with LAFB in women with CVD the risk. The risk for CHD death was increased over threefold (HR 3.09, CI 1.26–7.58) and over twofold for total mortality (HR 2.69, CI 1.55–4.67). And for IVCD the risk for CHD death was increased significantly for women with CVD (HR 2.52, CI 1.34–4.75).
8.2.1 Repolarization Abnormalities and Mortality Risk in Ventricular Conduction Defects
In the above study [2] QRS duration was entered simultaneously with QRS|T angle and other repolarization parameters as covariates. QRS duration was not a significant independent predictor of CHD death. None of the repolarization parameters were significant independent ECG predictors of CHD death in RBBB. In LBBB, ST J-point depression in aVL was a markedly strong independent predictor of CHD mortality with an over fivefold increased risk in fully-adjusted risk model. This was the first study which evaluated mortality risk associated with repolarization parameters as covariates in LBBB and RBBB.
8.3 Independent Predictors for Heart Failure in Left Bundle Branch Block and Right Bundle Branch Block
HF risk data for independent ECG predictors of HF in CHD-free women and in women with CVD at baseline reproduced in Table 8.2 from the report of Zhang et al. [3] reveals some interesting associations for HF risk in multivariable-adjusted models.
Table 8.2
Significant independent ECG predictors of incident heart failure in women for baseline LBBB and RBBB
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